This invention relates generally to transformers and is particularly directed to an arrangement for mounting a multi-winding transformer on a printed circuit (PC) board and coupling various circuit components to the transformer.
In a conventional raster scanned video display incorporating a cathode ray tube (CRT) such as a television receiver or a computer terminal, a rectified and regulated AC line voltage is provided to a primary winding of a high voltage sweep transformer. The sweep transformer includes a primary winding as well as a plurality of secondary windings such as pulse and high voltage secondary windings which are electromagnetically coupled to the primary winding for developing various output voltages for operation of the video display device. For example, a high voltage is provided to the CRT's anode for accelerating the electrons emitted by its cathode, while the pulse windings provide various output pulses required for such functions as phase control of CRT raster scan with the video signal and ensuring a horizontal distortion-free video image. These output pulses may also be rectified to provide various DC voltages required for the operation of other circuits. For example, in a computer terminal several DC voltage levels may be required for such functions as powering logic circuitry, driving computer peripherals, etc. Rectifying diodes are typically coupled across the secondary windings of the sweep transformer for generating these various DC outputs. The DC output voltages are then provided to various terminal pins typically positioned on one end of the bobbin, which pins are adapted for coupling to DC driven output circuits.
Referring to FIG. 1, there is shown a partially cutaway lateral view of a prior art transformer 10. The transformer 10 includes a second outer bobbin 14 coaxially disposed about a first inner bobbin 12. The first inner bobbin 12 includes a plurality of flanges or ribs 22 between which are disposed a primary winding 26. The second outer bobbin 14 similarly includes a plurality of laterally extending ribs between which are disposed in a wound configuration various secondary windings 30. The various secondary windings 30 are coupled to a plurality of terminal pins 34 which are positioned on one end of the second outer bobbin 14. An end portion 24 of one of the secondary windings is shown coupled to one of the terminal pins 34 by conventional means such as soldering. A ferrite core 16 comprised of two U-shaped core sections 18, 20 is adapted for insertion within the first inner bobbin 12 and along the length of the second outer bobbin 14. Although only one is shown in the figure, a plurality of diodes 32 are coupled across respective ends of each of the secondary windings 30 to provide a rectified output from a secondary winding to the terminal pins 34. Terminal pins 34 are typically inserted in apertures on a PC board and are thus coupled in circuit with various components positioned thereon, although this is not shown in the figure for simplicity.
These diodes are typically coupled across respective pairs of connector or terminal pins 36 extending outward from a lateral portion of the second, outer transformer bobbin, with the number of diodes determined by the number of secondary windings positioned on the bobbin. These diodes are generally coupled to the terminal pins by hand soldering in a labor intensive, time consuming and expensive process. In addition, this procedure for transformer assembly is subject to various errors such as coupling a diode of the wrong rating to respective ends of a secondary winding, reversing the direction of the diode in circuit, or coupling a diode to respective ends of two different secondary windings. Moreover, the manual nature of this assembly procedure reduces the reliability of the electrical connection because of the human factor.
The present invention overcomes the aforementioned limitations of the prior art by providing a sweep transformer with a terminating PC board which is low cost and simple in construction and is particularly adapted for automatic assembly and mounting in circuit on a PC board.